Hey...this problem arose: A force of 40N is required to start a 5 kg box moving across a horizontal concrete floor. A) What is the coefficient of static friction between the box and the floor? (its .82, I got this no problem) B) If the 40N force continues, the box accelerates at 0.7 m/s^2. What is the coefficient of kinetic friction? I don't see how to do part B. I know it's .74, but I don't know how. Please explain in detail by showing equation(s).